1. Field of the Invention
This invention relates to ultrasound imaging systems and, more particularly, to systems having beamforming electronics.
2. Background Art
Real time 3D ultrasound imaging for medical applications requires housing an array of perhaps several thousand transducer elements and associated signal processing electronics in a hand-held probe unit. In smaller systems (e.g., having only a few hundred array elements) it has been conventional to carry the transducer signals through a multi-wire cable to a system console containing essentially all of the processing circuitry for image generation. However, with larger arrays containing transducer elements numbering in the thousands, or in the tens of thousands or even more, it is difficult and impractical to perform all of the signal processing in a remote unit. This would require dedicated leads, each forming a separate connection between a transducer element and processing circuitry located in the console. To address this problem, a limited portion of the processing circuitry has been placed in the probe. For example, a large array of transducer elements may be divided into subarrays of uniform size, e.g., ranging from 10 to 40 transducer elements, with a dedicated unit of beam forming and processing circuitry for each subarray, herein referred as a subarray circuit unit. Each subarray circuit unit can combine the signals generated by all of the transducer elements in the subarray into a single channel or wire, e.g., by analog beam-formation. With this or other configurations, the signals received from all of the elements in the array can be transferred via a reduced number of cable leads to the processing circuitry in the console. In this way the thousands of signals can be transferred while retaining a manageable cable size.
To effect circuit functions in the probe, each subarray circuit unit normally includes high voltage transmitter circuitry, low voltage receiver circuitry and digital control circuitry. Implementation of these different circuit functions has required fabrication of multiple integrated circuits, e.g., Application Specific Integrated Circuits (ASICs), because the differing circuit functions have required different semiconductor manufacturing processes. The multiple ASIC components required for all of the subarray circuits have consumed a relatively large volume of available space in the probe unit. With the impracticality of fabricating all three functions in one monolithic die, the volume required for housing these subarray circuit units can be a factor limiting the practical size of a transducer array housed in a hand-held probe unit. Size and weight considerations influence the ease with which the hand-held probe unit can be maneuvered during examination procedures.
The need to reduce size and weight of probe units and consoles is especially relevant to portable ultrasound imaging systems which may be configured with note-book computer systems. Generally, size and weight are constraining factors which can limit achievable image quality of systems which use portable, hand-held probe units. Consequently, many hand-held probe units employ a relatively low number of transducer elements in order to minimize the amount of wiring and circuitry and thereby meet these criteria. Yet it is recognized that improved image quality can increase the diagnostic utility of these systems.